Reason number one:For pump&dump purposes.
Reason number two:Exit scam ICO(which is kinda like the first one,but with pump&dump they could pump the coin again and gain aditional profits).
Those are the real reasons.The fake reasons include:instant and cheaper transactions,easy and profitable mining,technology innovation that will beat the crypto competition.
When I saw the title then thought same reason for that. Yeah so many useless and no needed new crypto currencies born every day for that reasons mostly. 95% of that currencies will die and only "just" 5% of them will survive.